Anatomy and Physiology of Pain Principles of Pain Spinal Cord Stimulation Intrathecal Drug Delivery Selective Spinal Cord Lesioning Neuroanesthesia

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The goal of programming
The primary goal of programming is to establish, for each patient, the drug dose that achieves optimal pain control, without causing intolerable adverse effects. This personalized drug dosage will vary with each patient. SynchroMed® is a fully implantable programmable drug delivery system. Programming of SynchroMed® is carried out with the N’Vision™ programmer.
When to program the SynchroMed® Pump
There are three occasions that require the pump to be programmed:
● A pump purge will need to be programmed in the operating room before the pump is implanted to ensure that the pump is fully operational
● A priming bolus and initial infusion mode will need to be programmed in the recovery room following implantation
● The pump will need to be reprogrammed as needed during routine follow-up appointments, refill appointments and/or any occasion that a change in drug dose is required

Programming the pump
After the SynchroMed® pump is implanted, the patient is transported to the recovery room, where the physician will program the pump. Programming allows the physician to enter the exact protocol for drug delivery and helps prevent overdose.
The following functions need to be set and/or altered by the clinician on the SynchroMed® pump:
● Date and time current prescription was entered
● Patient identification
● Drug name, concentration and dose
● Infusion mode
● Reservoir volume and low reservoir alarm setting (audible)
● Low battery alarm (audible) control

The two specific parameters that the physician will need to program postimplant are:
● The initial infusion rate
● The priming bolus dose
The initial infusion rate
The initial infusion rate is the rate at which the drug will be delivered. The infusion rate is automatically calculated by N’VisionTM based on the drug concentration.
The priming bolus dose
After implantation, the catheter and pump will have a segment that is not filled with the drug. The unfilled segment is called dead space. If the dead space is not filled, the first doses will only serve to fill the dead space, and the patient will not receive immediate pain relief. The priming bolus dose is intended to fill the dead space with the drug.
The priming bolus dose is calculated using the total drug volume of the tubing. Total drug volume of the tubing depends on:
● The pump tubing volume
● The length of the catheter
The calculation to determine the priming bolus, which is automatically performed by N’Vision™, is as follows:
Total drug volume of the tubing and implanted catheter (mL) x drug concentration (mg/mL) = priming bolus dos (mg)
Infusion modes
Infusion modes specify what drug dose will be delivered at what rate per hour or day, and for what duration. The SynchroMed® pump can be programmed to deliver medication at infusion rates ranging from 0.002 mL/hour to 0.9 mL/hour. There are a total of six infusion modes available with SynchroMed®:
● Stopped pump
● Single bolus
● Simple continuous
● Single bolus + Simple continuous
● Periodic bolus
● Complex continuous
● Simple continuous + PTM

Figure 1: Settings for the SynchroMed® pump on the N’Vision™ programmer

Patients can also initiate the delivery of physician-prescribed supplemental doses of intrathecal medication via the SynchroMed® Personal Therapy Manager, a patient operated hand-held device that communicates with the SynchroMed® pump via telemetry.
The modes are either Single-Cycle or Continuous-Cycle:
● Single-Cycle delivers one specific drug dose
● Continuous-Cycle delivers medication continuously over a specific period of time at a specified rate of infusion

Table 1: A description of the Infusion modes available with SynchroMed®

Single cycle Description
Stopped pump ● Turns the pump OFF, ceasing drug delivery
Single bolus ● Delivers a specific dose over a specified period of time, then reverts to the Stopped Pump Mode
Simple Continuous ● Delivers a continuous infusion of a specific amount of drug per day
Single bolus + Simple Continuous ● Combines the Single bolus and Simple continuous prescriptions
● Delivers a Single bolus prescription; when completed, the Simple continuous prescription begins. The Single bolus prescription is not repeated
Periodic bolus ● Delivers a specific amount of drug at the maximum rate, then delivers at the minimum rate for the specific delay period. These rates cannot be changed.
Complex Continuous ● Delivers a sequence of two to ten steps. When the last step is completed, the cycle repeats beginning with step one.
● Each step prescribes the dose, rate and duration. A 24-hour pattern is usually programmed

The Medtronic N’Vision™ programmer
The Medtronic N’Vision™ clinician programmer, which is a small, lightweight portable unit, allows physicians to non-invasively programme the implanted SynchroMed® pump, setting the infusion parameters of an individual patient’s medication prescription. N’Vision™ communicates with SynchroMed® via telemetry. The various settings on SynchroMed® can be changed by simply touching the programmer’s screen with a stylus.
N’Vision™ has been designed to simplify patient management by the inclusion of several innovative features:
● Convenient automatic calculation of priming and bridge bolus for ease of use
● Offers both touch-screen and Windows-like software designed to simplify programming
● Stores up to 100 patient session files, as well as basic data on up to 1000 patients
● Provides the flexibility to print to a standard desktop printer with infrared printing support, or to the N’Vision™ portable printer
SynchroMed® pump refill and refill intervals
A refill appointment usually includes:
● An assessment of the patient’s general condition and response to therapy
● Programming the pump
● Refilling the pump
● Determining the interval to the next refill
● Scheduling the next refill appointment
Refilling the pump
Once patients receive SynchroMed®, their doctor will periodically refill the pump with medication. This is done by inserting a needle through the skin into the pump’s reservoir.
Determining a refill schedule
The physician will also need to determine refill intervals. Refill intervals are carefully calculated to prevent depletion of the drug reservoir. The N’VisionTM physician programmer automatically calculates the refill intervals. Refill intervals are typically every 1–3 months. However, this may vary depending on the individuals prescription. For those patients with a continuous pump, the physician will calculate the refill interval as follows:
[Drug concentration x usable reservoir volume]/ Daily dose.

What’s New
Inomed ISIS Intraoperative neurophysiological monitoring started to function in all our related surgeries.
Oct /07/2009
The author celebrating 30 years experience in neurosurgery.
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